Charge-Separated Metal-Organic Frameworks Derived from Boron Centered Tetrapods

Metal-organic frameworks (MOFs) are an emerging class of microporous materials that have potential applications in a wide range of areas. As a sub-class of MOFs, ionic MOFs, especially charge-separated MOFs, have been relatively less studied but possess unique features including strong host-guest interactions from the exposed charged centers. We report the synthesis and single-crystal structural characterization of five new charge-separated MOFs (UNM 1-5) based on two tetrapodal borate ligands: tetrakis(4-(4-pyridineethynyl)-2,3,5,6-tetrafluorophenyl)borate (T1) and tetrakis(4-(4-pyridyl)-2,3,5,6-tetrafluorophenyl)borate (T2) having rigid arms of different lengths and pyridine groups at the end of each arm. Coordination of these tetrapods with Cu(I), Cu(II), and Ag(I) ions under specific conditions led to a series of new charge-separated MOFs in single crystalline forms. UNM-1 and UNM-2/UNM-3, which crystalize respectively in tetragonal I-4 space group and monoclinic C 2/c space group, are derived from Cu...